This invention relates to long term stabilization of an enzyme contained in an aqueous composition by a lower molecular weight organic ester.
The desirability of using enzymes of the proteolytic and alpha amylolytic type in cleaning compositions is well known. These enzymes are useful for their ability to reduce macromolecules such as proteins and starches into smaller molecules so that they can be readily washed away by detergents and/or water. Specifically, the proteolytic enzymes are useful in breaking down proteins and the alpha amylolytic enzymes are useful in breaking down carbohydrates. Detergent compositions containing these enzymes have a wide variety of uses in that they are capable of removing proteinaceous and starchy stains such as egg stains, blood stains, gravy stains, and the like.
Detergent compositions containing enzymes have been commercially available in dry powdered form. However, there are inherent problems with these compositions. First, they must be stored in such a way as to be protected from humidity and high heat to insure enzyme stability. Second, these dry powdered compositions are not well suited for several useful applications such as spot cleaners, laundry presoaks and prespotters, which require direct application to the stained surface. For these and other applications it is desirable to have a liquid enzyme composition. It is also advantageous to include significant amounts of water in liquid enzyme compositions for economic as well as processing considerations. However, an inherent problem exists in adding significant amounts of water to an enzyme containing composition in that enzymes are inherently unstable in the presence of water resulting in a rapid decrease of enzymatic activity, i.e., the ability of the enzyme to effectively reduce macromolecules into smaller molecules. It is speculated that the loss in enzymatic activity is due to the hydrolyzing action of water on the enzyme.
Further decreases in enzymatic activity will also result from exposing the aqueous enzyme containing compositions to temperatures in excess of 70.degree. C. In fact, if these compositions are exposed to these temperatures for more than a few hours, complete deactivation will occur.
Therefore, in order to have an aqueous based enzyme containing composition which is suitable for the uses described above, it is clear that the enzyme must not only remain stable in water, i.e. retain its enzymatic activity, but it must also be capable of maintaining such stability for extended periods of time at elevated temperatures, i.e., up to about 100.degree. F. It is not uncommon to have commercial products stored in warehouses for a period of time before being sold to consumers, where the temperatures during storage may exceed normal room temperature.
Various attempts have been made to stabilize enzymes contained in aqueous compositions. The following are exemplary of these.
U.S. Pat. No. 3,296,094 to Cayle utilizes a partially hydrolyzed and solubilized collagen, and glycerol to stabilize an aqueous proteolytic enzyme composition. The amount of glycerol required for stabilization in this composition is between 35% to 60% by weight of the total composition.
U.S. Pat. No. 3,557,002 to McCarty utilizes a monohydroxy alcohol or an alkoxy alcohol to stabilize a proteolytic enzyme. Although the amount of alcohol used in this composition is less than that used in Cayle the residual activity of the enzyme of this composition decreases after long periods of storage at relatively high temperatures.
U.S. Pat. No. 4,169,817 to Weber utilizes either water soluble salts such as sodium or potassium sulfates or chlorides and/or glycerol or alkylene glycols to stabilize a proteolytic enzyme in compositions containing ionic builders and surfactants. Again, significant amounts of glycerol and/or other solids are required to maintain long term enzyme stability in these compositions.
U.S. Pat. No. 3,682,842 to Innerfield utilizes a composition comprising an enzyme-ion binding agent such as trichloroacetic acid or tungstic acid and at least two of: a salt, such as sodium chloride or ammonium sulfate; an organic solvent such as ethanol, and an anionic surfactant, to stabilize a mixture of proteolytic and amylolytic enzymes.
U.S. Pat. No. 3,676,374 to Zaki et al utilizes a mixture of alkane sulfonates or alpha olefin sulfonate compounds, along with an alkyl alkyleneoxy hydroxyl or sulfate compounds to stabilize a proteolytic enzyme in a liquid detergent composition containing water. Additionally, various stabilizing agents can be employed with these compositions such as the water-soluble calcium and magnesium chloride lactates and acetates.
Barrett, Jr., in U.S. Pat. No. 3,746,649 discloses a liquid enzyme product stable against proteolytic degradation, the product consisting essentially of an enzyme and 100 to 500 parts per part of the enzyme of an organic medium free of glycerine, the medium being selected from the group of certain of the following: alcohols; alkylene glycols; alkylene glycol alkyl or phenyl ethers; alkylene glycol esters; alkoxy ethanols, propanols and triglycols, and ketones.
In U.S. Pat. No. 3,953,353 to Barrett, Jr., et al, a solid product for rub-on application is disclosed. In U.S. Pat. No. 4,111,855, Barrat et al discloses a liquid enzyme containing detergent composition containing as the stability enhancing system 0.05 to 1.5% by weight of a polyacid capable of forming water-soluble Ca-complexes; from 0.5 to 15 millimol/liter of free calcium ions, and a liquid carrier of water and a lower aliphatic alcohol. The '855 Barrat et al patent teaches that the enzyme stability for a given level of polyacid is inversely related to the logarithm of the stability constant of the Ca-polyacid complexes at the pH of the composition.
Applicant herein, in his earlier issued U.S. Pat. No. 4,243,546 teaches that an alkanolamine in combination with an organic or inorganic acid improves the enzyme stability of aqueous enzyme containing detergent compositions. In Shaer copending patent application U.S. Ser. No. 414,552, filed Sept. 3, 1982, which application is a continuation of U.S. Ser. No. 173,779 filed July 30, 1980, now abandoned, the applicant herein discloses stabilization of enzyme containing detergent compositions with a stabilizer system containing a salt of a low molecular weight carboxylic acid in the presence of an alkyl alcohol of from one to six carbon atoms.
U.S. Pat. No. 4,287,082 to Tolfo discloses that homogeneous aqueous enzyme containing liquid detergent compositions containing substantial levels of saturated fatty acids may be stabilized with minute amounts of enzyme accessible calcium, and additive levels of selected short chain carboxylic acids. Similarly, Letton in U.S. Pat. No. 4,318,818 discloses a stabilizing system comprising calcium ions and a low molecular weight carboxylic acid or salt, preferably a formate, and preferably in the presence of a low molecular weight alcohol, the pH being in the range of from about 6.5 to about 10.
Stabilization of enzyme containing compositions is also discussed in U.S. Pat. Nos. 3,600,318 to Mast; 4,261,868 to Hora et al; 4,142,999 to Bloching et al; 4,243,543 to Guilbert et al; 3,532,599 and 3,813,342 to Cooperman; 3,869,399 to Collins; 3,575,864 to Innerfield, and 3,023,168 to Doan.
In U.S. Pat. No. 3,532,599 to Cooperman, a cleaning composition is disclosed for removing printing ink from rubber rollers, the composition optionally including any inert diluent that does not deactivate the enzyme. The organic solvents that may be included include aromatic solvents, e.g., benzene, aliphatic hydrocarbons such as hexane, or other solvents such as ethanol ethyl acetate or ether. No discussion is provided concerning the effect of these solvents or diluents on stability. Rather, Cooperman states that the enzyme is compatible with these materials.